This invention relates generally to a multiservice antenna system assembly. The multiservice antenna system assembly may include one antenna that is fastened by means of a support, or at least two antennas that are grouped together by means of a support. The support may, for example, be a plastic packing. This invention is particularly useful when the antenna assembly is located in automobile rear-view mirrors and more particularly in exterior rear-view mirrors, but may also have utility in other applications.
Until recently, the telecommunication services included in an automobile were limited to a few systems, mainly the analogical radio reception (AM/FM bands). The most common solution for these systems is the typical whip antenna mounted on the car roof. The current tendency in the automotive sector is to reduce the aesthetic and aerodynamic impact of such whip antennas by embedding the antenna system in the vehicle structure. Also, a major integration of the several telecommunication services into a single antenna is specially attractive to reduce the manufacturing costs or the damages due to vandalism and car wash systems.
The antenna integration is becoming more and more necessary as we are assisting to a deep cultural change towards the information society. The internet has evoked an information age in which people around the globe expect, demand, and receive information. Car drivers expect to be able to drive safely while handling e-mail and telephone calls and obtaining directions, schedules, and other information accessible on the world wide web (WWW). Telematic devices can be used to automatically notify authorities of an accident and guide rescuers to the car, track stolen vehicles, provide navigation assistance to drivers, call emergency roadside assistance and remote diagnostics of engine functions.
The inclusion of advanced telecom equipments and services in cars an other motor vehicles is very recent, and it was first thought for top-level, luxury cars. However, the fast reduction in both equipment and service costs are bringing telematic products into mid-priced automobiles. The massive introduction of a wide range of such a new systems would generate a proliferation of antennas upon the bodywork of the car, in contradiction with the aesthetic and aerodynamic trends, unless an integrated solution for the antennas is used.
On the other hand FIG. 11 shows examples of space filling curves. Space filling curves 1501 through 1514 are examples of prior art space filling curves for antenna designs. Space filling curves fill the surface or volume where they are located in an efficient way while keeping the linear properties of being curves.
Among other possible definitions a Space-filling curve could be defined as a non-periodic curve composed by a number of connected straight segments smaller than a fraction of the operating free-space wave length, where the segments are arranged in such a way that none of said adjacent and connected segments form another longer straight segment and wherein none of said segments intersect to each other.
FIGS. 13-22 shows an example of how the grid dimension is calculated. The grid dimension of a curve (See FIG. 13) may be calculated as follows: A first grid (1700) having square cells of length L1 is positioned over the geometry of the curve such that the grid completely covers the curve. The number of cells (N1) in the first grid that enclose at least a portion of the curve are counted. Next, a second grid (1800) (FIG. 14) having square cells of length L2 is similarly positioned to completely cover the geometry of the curve, and the number of cells (N2) in the second grid that enclose at least a portion of the curve are counted. In addition, the first and second grids should be positioned within a minimum rectangular area enclosing the curve, such that no entire row or column on the perimeter of one of the grids fails to enclose at least a portion of the curve. The first grid preferably includes at least twenty-five cells, and the second grid preferably includes four times the number of cells as the first grid. Thus, the length (L2) of each square cell in the second grid should be one-half the length (L1) of each square cell in the first grid. The grid dimension (Dg) may then be calculated with the following equation:
      D    g    =      -                                        log            ⁢                                                  ⁢                          (                              N                ⁢                                                                  ⁢                2                            )                                -                      log            ⁢                                                  ⁢                          (                              N                ⁢                                                                  ⁢                1                            )                                                            log            ⁢                                                  ⁢                          (                              L                ⁢                                                                  ⁢                2                            )                                -                      log            ⁢                                                  ⁢                          (                              L                ⁢                                                                  ⁢                1                            )                                          .      
For the purposes of this application, the term grid dimension curve is used to describe a curve geometry having a grid dimension that is greater than one (1). The larger the grid dimension, the higher the degree of miniaturization that may be achieved by the grid dimension curve in terms of an antenna operating at a specific frequency or wavelength. In addition, a grid dimension curve may, in some cases, also meet the requirements of a space-filling curve, as defined above. Therefore, for the purposes of this application a space-filling curve is one type of grid dimension curve.
FIG. 12 shows an example two-dimensional antenna (1600) forming a grid dimension curve with a grid dimension of approximately two (2). FIG. 13 shows the antenna (1600) of FIG. 12 enclosed in a first grid (1700) having thirty-two (32) square cells, each with a length L1. FIG. 14 shows the same antenna (1600) enclosed in a second grid (1800) having one hundred twenty-eight (128) square cells, each with a length L2. The length (L1) of each square cell in the first grid (1700) is twice the length (L2) of each square cell in the second grid (1800) (L2=2×L1). An examination of FIG. 14 and FIG. 15 reveal that at least a portion of the antenna (1600) is enclosed within every square cell in both the first and second grids (1700), (1800). Therefore, the value of N1 in the above grid dimension (Dg) equation is thirty-two (32) (i.e., the total number of cells in the first grid 801), and the value of N2 is one hundred twenty-eight (128) (i.e., the total number of cells in the second grid (802). Using the above equation, the grid dimension of the antenna 800 may be calculated as follows:
      D    g    =            -                                    log            ⁢                                                  ⁢                          (              128              )                                -                      log            ⁢                                                  ⁢                          (              32              )                                                            log            ⁢                                                  ⁢                          (                              2                ×                L                ⁢                                                                  ⁢                1                            )                                -                      log            ⁢                                                  ⁢                          (                              L                ⁢                                                                  ⁢                1                            )                                            =    2  
For a more accurate calculation of the grid dimension, the number of square cells may be increased up to a maximum amount. The maximum number of cells in a grid is dependant upon the resolution of the curve. As the number of cells approaches the maximum, the grid dimension calculation becomes more accurate. If a grid having more than the maximum number of cells is selected, however, then the accuracy of the grid dimension calculation begins to decrease. Typically, the maximum number of cells in a grid is one thousand (1000).
For example, FIG. 15 shows the same antenna 1600 enclosed in a third grid 1900 with five hundred twelve (512) square cells, each having a length L3. The length (L3) of the cells in the third grid 1900 is one half the length (L2) of the cells in the second grid 1800, shown in FIG. 18. As noted above, a portion of the antenna 1600 is enclosed within every square cell in the second grid 1800, thus the value of N for the second grid 1800 is one hundred twenty-eight (128). An examination of FIG. 8D, however, reveals that the antenna 800 is enclosed within only five hundred nine (509) of the five hundred twelve (512) cells of the third grid 1900. Therefore, the value of N for the third grid 1900 is five hundred nine (509). Using FIG. 8C and FIG. 8D, a more accurate value for the grid dimension (D) of the antenna 800 may be calculated as follows:
      D    g    =            -                                    log            ⁢                                                  ⁢                          (              509              )                                -                      log            ⁢                                                  ⁢                          (              128              )                                                            log            ⁢                                                  ⁢                          (                              2                ×                L                ⁢                                                                  ⁢                2                            )                                -                      log            ⁢                                                  ⁢                          (              L2              )                                            ≈    1.9915  
FIGS. 16 and 17 shows an alternative example of how the box counting dimension is calculated. The antenna comprises a conducting pattern, at least a portion of which includes a curve, and the curve comprises at least five segments, each of the at least five segments forming an angle with each adjacent segment in the curve, at least three of the segments being shorter than one-tenth of the longest free-space operating wavelength of the antenna. Each angle between adjacent segments is less than 180° and at least two of the angles between adjacent sections are less than 115°, and wherein at least two of the angles are not equal. The curve fits inside a rectangular area, the longest side of the rectangular area being shorter than one-fifth of the longest free-space operating wavelength of the antenna.
One aspect of the present invention is the box-counting dimension of the curve that forms at least a portion of the antenna. For a given geometry lying on a surface, the box-counting dimension is computed in the following way: First a grid with boxes of size L1 is placed over the geometry, such that the grid completely covers the geometry, and the number of boxes N1 that include at least a point of the geometry are counted; secondly a grid with boxes of size L2 (L2 being smaller than L1) is also placed over the geometry, such that the grid completely covers the geometry, and the number of boxes N2 that include at least a point of the geometry are counted again. The box-counting dimension D is then computed as:
  D  =      -                            log          ⁢                                          ⁢                      (                          N              ⁢                                                          ⁢              2                        )                          -                  log          ⁢                                          ⁢                      (                          N              ⁢                                                          ⁢              1                        )                                                log          ⁢                                          ⁢                      (                          L              ⁢                                                          ⁢              2                        )                          -                  log          ⁢                                          ⁢                      (                          L              ⁢                                                          ⁢              1                        )                              
In terms of the present invention, the box-counting dimension is computed by placing the first and second grids inside the minimum rectangular area enclosing the curve of the antenna and applying the above algorithm.
The first grid should be chosen such that the rectangular area is meshed in an array of at least 5×5 boxes or cells, and the second grid is chosen such that L2=½ L and such that the second grid includes at least 10×10 boxes. By the minimum rectangular area it will be understood such area wherein there is not an entire row or column on the perimeter of the grid that does not contain any piece of the curve. Thus, some of the embodiments of the present invention will feature a box-counting dimension larger than 1.17, and in those applications where the required degree of miniaturization is higher, the designs will feature a box-counting dimension ranging from 1.5 up to 3, inclusive. For some embodiments, a curve having a box-counting dimension of about 2 is preferred. For very small antennas, that fit for example in a rectangle of maximum size equal to one-twentieth of the longest free-space operating wavelength of the antenna, the box-counting dimension will be necessarily computed with a finer grid. In those cases, the first grid will be taken as a mesh of 10×10 equal cells, while the second grid will be taken as a mesh of 20×20 equal cells, and then D is computed according to the equation above. In the case of small packages with of planar designs, i.e., designs where the antenna is arranged in a single layer on a package substrate, it is preferred that the dimension of the curve included in the antenna geometry have a value close to D=2.
In general, for a given resonant frequency of the antenna, the larger the box-counting dimension the higher the degree of miniaturization that will be achieved by the antenna. One way of enhancing the miniaturization capabilities of the antenna according to the present invention is to arrange the several segments of the curve of the antenna pattern in such a way that the curve intersects at least one point of at least 14 boxes of the first grid with 5×5 boxes or cells enclosing the curve. Also, in other embodiments where a high degree of miniaturization is required, the curve crosses at least one of the boxes twice within the 5×5 grid, that is, the curve includes two non-adjacent portions inside at least one of the cells or boxes of the grid.
The placement of a multiservice antenna system in certain position of the vehicle, such as a exterior rearview mirror is advantageous for many reasons. For example, reception and transmission of the signal is improved. In addition the antenna may be delivered to the car manufacturer already mounted meanwhile the antenna remains hidden in order to enhance the aesthetic of the vehicle.
Certain parts of the vehicle must endure difficult mechanical conditions such as vibration, moisture environments and difficult grounding of electrical components. The multiservice antenna system disclosed herein may help to overcome problems associated with placement of a multiservice antenna system assembly in difficult environments either because mounting difficulties and/or extreme physical conditions such as vibration or moisture. For example, the following features may be included in a multiservice antenna system which help to overcome problems associated with mounting the antenna in difficult environments:                integration of the radio AM/FM antenna and the related active system of the same physical support (FR4 in this case),        the design of a plastic part to ensure waterproof protection of the active system components, fixation and position of the antennas respect to the other parts of the mirrors, ensure no damage during the part handlings,        an adequate grounding of the different antennas integrated in the mirror to optimize the antenna performance and reduce the interference noise due to other devices,        a correct separation and position in the same plane between the radio and telephone antennas, and        the capacity to integrate 3 antennas services into the same external mirror        
One aspect of the invention refers to a multiservice antenna system assembly, which comprises at least one antenna wherein each antenna is supported by a support member.
At least one antenna of the assembly is placed on a face of a printed circuit board which is fixed to said support member. Preferably, said printed circuit board is at least partially embedded within said support member.
At least one antenna of the antenna system assembly is at least partially shaped as a space-filling curve or a grid-dimension curve, which preferably features a box-counting dimension or a grid dimension larger than 1.5, or larger than 1.9.
The multiservice antenna system assembly, provides radio communication services, telephone communication services, GPS positioning service, or any combination of said services. For that purpose, the antenna assembly may comprises a second printed circuit board including a telephone antenna, which is supported on said support member and is placed perpendicularly with respect to said first printed circuit board. Preferably, said telephone antenna is a GSM dual band antenna or a multiband antenna for cellular telephony.
Other aspect of the invention refers to a rear-view mirror assembly for a vehicle, which is conventionally formed by one or two mirrors attached to a protective case. The mirror assembly includes the multiservice antenna system assembly object of the present invention.